1. Field of the Invention
The present invention relates to an auto-stereoscopic display system and auto-stereoscopic display device for inclusion in such a system.
2. Background Description
Three dimensional or stereoscopic images may be produced via holographic, volumetric, or multi-view techniques. A conventional multi-view technique involves viewing a frame sequential pair of images with specially adapted glasses. Specifically, a display device present alternate left and right views to the observer on a frame sequential basis. The glasses worn by the observer effectively route the views to each eye. Shutters or polarisers in the glasses are synchronised to the frame rate to control the routing. To prevent flicker, the frame rate must be doubled or the resolution halved with respect to the two dimensional equivalent image. A disadvantage with such as system is that the two images produce only a limited "look around" capability. Furthermore, glasses have to be worn to produce any effect.
Another conventional multi-view technique involves a barrier auto-stereoscopic display system. In some examples of such a system, a stereo pair of images is sliced into vertical strips. The strips of each image of the pair are meshed together on the display screen. A physical barrier is placed in front of the display screen. Small viewing zones are formed in the barrier so that the left eye can see only strips of the first image of the pair and the right eye can see only strips of the second image of the pair. The observer re-constructs the full image in three dimensions. A disadvantage with this arrangement is that the viewing zone is very narrow. Outside the zone, the observer sees multiple images or a stereo inversion. Furthermore, there is no "look around" effect. In a modification to the physical barrier system, the barrier is replaced by a lenticular lens screen having an array of vertical cylindrical lenses each corresponding to a different pair of left and right view strips.
The lenticular screen approach can be enhanced by assigning further image strips to each lens. For example, if each lens corresponds to four views (from four cameras instead of two) then repeating double viewing zones are generated instead of the repeating single viewing zone associated with the basic method described earlier. If the observer moves to the left of the display screen, a new image, to left of the previous image, is observed. The number of reverse stereo zones is reduced. Specifically, reverse stereo zones are produced only at the point where multiple zones repeat. The latitude of head movement is improved with increasing number of views. Each different view can be employed to simulate "look around" effects. A disadvantage with four view systems is that as the observer moves from the first view to the second view, the spatial resolution of the system causes a jump in continuity. In general, experiment suggests that 16 views are sufficient to produce satisfactory three dimensional viewing.
In an example of a conventional multi-view system, there is provided a 16 view time-multiplexed cathode ray tube (CRT) display comprising a slit shutter disposed at a distance of around 30 cm in front of the screen. A disadvantage with this time division arrangement is that the display system is required to operate at high CRT scan frequencies (greater than 150 kHz), very high EHT voltages (greater than 30 kV), and very fast phosphors. Furthermore, the spacing between the CRT and the shutter produces a cumbersome construction.
It is desirable in a multi-view lenticular system to display each view in relatively narrow stripes. The thickness of the stripe is dependent on the spot size of the display. Liquid crystal display (LCD) panels have a relatively large spot size. Relatively small spot sizes can be achieved in conventional CRTs. However, to achieve such spot sizes in a CRT, relatively high EHT voltages, fast video amplifiers, and fast phosphors are required, leading to added circuit complexity, power consumption, and manufacturing cost. Furthermore, for optimum results, the lenticular screen is preferably located close to a flat image source. The thickness and curvature of many conventional CRTs therefore renders them unsuitable.
It would be desirable to provide a new stereoscopic display technology in which the aforementioned problems associated with conventional stereoscopic display technologies such as LCD and CRT are solved.